The potential reserves of liquid hydrocarbons which are contained in subterranean carbonaceous deposits have been identified as being substantial. Tar sands and oil shales represent two of the major potential resources of oil. In fact, the potential reserves of liquid hydrocarbons to be derived from tar sands and oil shales is believed to exceed the known reserves of liquid hydrocarbons to be derived from petroleum. However, the exploration of these potential reserves has been limited by the previously low priced and abundant supply of liquid crude oil and the process difficulties of (a) extracting the heavier more viscous organic materials from tar sands and oil shales, and (b) converting the heavier materials to fuel range liquids.
More recently, however, because of the threat of increased costs of liquid crude oils and the ever present threat of reduced availability from foreign sources, there is significant interest in improving the economics of recovering liquid hydrocarbons and in particular, fuel range liquids from heavy hydrocarbon sources on a commercial scale. Methods have been suggested for recovering hydrocarbons from tar sands and oil shales, but the methods generally have not been accepted because of their high costs which renders recovered hydrocarbons too expensive to compete with petroleum crudes which can be recovered by more conventional methods. Heavy crude oils such as the California, Alaskan and Venezuelan crudes are difficult to transport through pipelines because of their high viscosity and pour points. Improved methods for reducing the pour points and the viscosity of heavy crude oils are desirable since lower viscosity results in higher pipeline throughput with less pressure drop and reduced energy consumption.
The extraction of oil from tar sands and oil shales requires a physical separation process to break the oil/sand or shale bond. Techniques include the use of hot water, steam and/or hot gases. Such a process requires high temperatures.
The crude oil produced from both tar sands and oil shales requires further processing to convert it to an acceptable refinery feedstock. The tar sands crude is a heavy extremely viscous high sulfur crude generally requiring that it be coked and hydrogenated or alternatively, hydrocracked. The oil recovered from shale retorts is similar to conventional crudes in some respects and is extremely viscous and contains a high nitrogen content.
The value of the hydrocarbons which have been recovered from oil shale and tar sands also has been diminished due to the presence of certain contaminants such as sulfur, nitrogen, and metallic compounds which have a negative effect on the catalyst utilized in many of the processes to which the recovered hydrocarbons may be subjected. The contaminants also are undesirable because of their disagreeable odor, corrosive characteristics and combustion products.
Petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum also are characterized by relatively high concentrations of metals, sulfur and nitrogen. The high level of impurity results because substantially all of the contaminants present in the original crude remain in the residual fraction. The high metals content of the residual fractions generally preclude their effective use as charge stocks for subsequent catalytic processing because the metal contaminants deposit on the special catalyst for the processes and also result in the formation of inordinant amounts of coke, dry gas and hydrogen. For example, the delayed coking process has been effected on heavy residium fuels to obtain lower boiling cracked products. The process is considered a high severity thermal cracking process and yields large amounts of coke by-product.
Methods have been suggested for recovering liquid hydrocarbon fractions from various carbonaceous deposits utilizing water and in particular, supercritical water which results in increased yields of distillate and decreased levels of coke relative to straight pyrolysis. U.S. Pat. No. 3,051,644 discloses a process for the recovery of oil from oil shale which involves subjecting the oil shale particles dispersed in steam to treatment with steam at temperatures in the range of from about 370.degree. C. to about 485.degree. C., and at a pressure in the range from about 1000 to 3000 psi. Oil from the oil shale is withdrawn in vapor form and admixed with steam. In U.S. Pat. No. 2,665,238, a process is described for recovering oil from oil shale which involves treating the shale with water in a large amount approaching the weight of the shale at a temperature in excess of 260.degree. C. and under a pressure in excess of 1000 psi. The amount of oil recovered increases generally as the temperature or pressure is increased.
U.S. Pat. No. 1,956,567 describes a process for aquolyzing petroleum products such as heavy hydrocarbons wherein the proportion of water that is used is considerably in excess of the proportion of oil that is used. The temperature and pressure in the reaction zone are above the critical temperature and pressure for water. U.S. Pat. No. 2,035,120 describes a process for converting heavy oil to light oils by treating oil with a large excess of water at high pressures and at temperatures above the critical temperature. U.S. Pat. No. 1,956,603 also relates to the aquolyzing of petroleum products, but the process described in this patent uses less water. The process of the '603 patent involves forming an emulsion of the heavy oil in water containing at least 50% water, and subjecting the emulsion to temperatures between 1000-1250.degree. F. at a pressure of about 200 atmospheres.
U.S. Pat. No. 2,135,332 describes a conversion of hydrocarbon oil to lighter hydrocarbons by subjecting the oil and a diluent gas (water or steam) to temperatures in the order of 960-975.degree. F. or more and pressures preferably about 2000 to 3000 psi. The amount of diluent gas should be in excess of 10% by weight of the original charging stock and preferably considerably more.
U.S. Pat, No. 3,989,618 describes a process for upgrading a hydrocarbon fraction by contacting the hydrocarbon fraction with a dense-water-containing fluid at a temperature in the range of 600-900.degree. F. in the absence of any externally supplied catalyst and hydrogen. The water-containing fluid used in the process has a density of at least 0.10 gram per milliliter and the fluid serves as an effective solvent for the hydrocarbon fraction. The process described in the '618 patent also is reported to be useful for recovering upgraded hydrocarbons from tar sand solids in U.S. Pat. No. 4,005,005.
U.S. Pat. No. 4,428,828 describes a process for upgrading oils in which the oil is contacted with liquid phase water and free oxygen at a temperature above 175.degree. C. and at a pressure sufficient to maintain at least part of the water in the liquid phase. The temperature generally is in the range of from 175.degree.-300.degree. C., and the aqueous liquid:hydrocarbon oil volume ratio may be from 0.5:1 up to about 10:1.
U.S. Pat. No. 4,604,188 describes the procedure for thermally upgrading residual oils by heating the oils with steam at a temperature of 650.degree.-900.degree. F. and 0-100 psig. The steam to residual oil ratio is 0.01 to 10, preferably from 0.1 to 1.
U.S. Pat. Nos. 4,483,761; 4,594,141; and 4,559,127 describe procedures for upgrading heavy hydrocarbons with supercritical water and various catalysts or promoters.
A procedure for the extraction of oil from shale and tar sands by supercritical water preferably containing dissolved salts is described in DE3201719(A). Temperatures of from 360.degree.-600.degree. C. and pressures of 130-700 atmospheres are described as being used, and the water preferably contains one or more dissolved salts, especially alkali, alkaline earth or ammonium chlorides or carbonates.